Poly(phenylene ether)s are a class of plastics known for excellent water resistance, dimensional stability, and inherent flame retardancy, as well as high oxygen permeability and oxygen/nitrogen selectivity. Properties such as strength, stiffness, chemical resistance, and heat resistance can be tailored by blending poly(phenylene ether)s with various other plastics in order to meet the requirements of a wide variety of consumer products, for example, plumbing fixtures, electrical boxes, automotive parts, and insulation for wire and cable.
Another use of poly(phenylene ether) is in the fabrication of solar thermal collectors. Solar thermal collectors are designed to absorb sunlight and convert it to thermal energy that can be used to heat buildings and to generate hot water at reduced cost. In general, polymer-based solar collectors are much less expensive than conventional copper flat plate collectors, and are therefore cost-effective even in regions where energy is relatively inexpensive. Extremely high temperatures can be realized in solar collectors, especially when heat transfer fluid is not present or is not circulating. Solar collectors comprise solar panels, solar connectors, and junction boxes. Solar connectors and junction boxes can operate at temperatures as high as 85° C., and solar panels can operate at temperatures as high as 140° C. The current maximum continuous use temperature for the most common poly(phenylene ether), poly(2,6-dimethyl-1,4-diphenylene ether) is about 125° C. Prolonged exposure to these high temperatures can accelerate oxidative degradation of the poly(phenylene ether), which can be accompanied by a loss of the physical properties which make it suitable for use in this application. Thus there remains a need in the art for poly(phenylene ether)s having increased resistance to thermal and oxidative degradation.
Japanese Unexamined Patent Publication JP 11-322921 of Kita et al. generally discloses a copolymer formed by oxidative copolymerization of 2-methylphenol and a second monohydric phenol than can be, among others, 2,6-dimethylphenol. However, there are no examples of copolymers of 2-phenylphenol and 2,6-dimethylphenol. Kita also discloses copolymers comprising 50-100 weight percent of 2-phenylphenol units and 0-50 weight percent of monohydric phenol units. When the monohydric phenol is 2,6-dimethylphenol, the weight ratios of Kita correspond to 41.8 to 100 mole percent of 2-phenylphenol. However, 2-phenylphenol is more expensive than 2,6-dimethylphenol, and the copolymers of Kita will be significantly more expensive to produce than poly(2,6-dimethyl-1,4-phenylene ether). Thus there remains a need in the art for poly(phenylene ether) copolymers having a good balance of thermal and oxidative stability and reduced cost.